Actually, Mastering Jujitsu by Renzo Gracie also states that much of judo groundwork comes from Fusen Ryu jiu-jitsu. Apparently judo orignall did not have ANY groundwork, but after a challenge match between the Kodokan and Fusen ryu (which resulted in Kodokan being completely defeated) Kano asked the grandmaster of Fusen ryu to teach groundwork to judokas.

I don't have the book with me in my dorm, so if anyone who does wants to put up a more detailed sypnosis then please do so.